Speaking as one of those non-religious types, I have to ask a question: Why do we need a religious figure to be included in the Inauguration of the President of the United States? I don't care about Rick Warren. He doesn't speak for me -- but then again, the Reverend Barry Lynn doesn't speak for me either (at least from a religious standpoint).
But if I were the leader of the LGBT band from San Francisco that is scheduled to perform in the Inaugural Parade, I might be tempted to inform Obama that they might be busy that day. You know, for a parade in South Dakota, perhaps.
I do think that Obama's response is pretty good, FWIW: